The Silent Whiskers came from Cathay where some members were living in the Great Wall of Cathay while others were living with various noble clans (of various races including humans) as part of the tradition of providing family members as hostages as of treaties.
Rats chosen to live with non-rat clans were usually from a select branch of the Silent Whiskers clan raised and educated to be able to live with non-rat clans without causing too much offence and also acted as the hosts for non-rats hostaged in return.
The clan members living in the Great Wall also contributed to the defence of the great wall. But also had a lot of trade dealings with white ghosts (people's from outside of Cathay)
Things were fine until a new emperor came to the throne. He believed the Silent Whispers had been dangerously influenced by foriegn ideals. A particularly important member of Silent Whiskers R'tiz'i-san (pronounced like "R-ik-tiz-ik-i-san") got framed and ended up up commiting Seppuko, which was unheard of for a rat as their sense of honour doesn't usually extend to anything like such extremes, but this rat had been born and raised in a non-rat clan as the son of a Silent Whiskers hostgae so had a more human-like view of honour, and also he was aware that this act of his would buy time for the rest of the clan to get out whereas if he'd refused then the whole clan would have been in danger.
Because of this act this rat has the very rare honour of rats voluntarily using the "-san" suffix when referring to him. Normally rats only use this suffix when they suspect that not using it will result in getting injured or killed!
To cut a long story short the Silent Whiskers built a flotilla and left Cathay together with various humans and a few fey - we don't know much about the humans' or the Fey's reasons for leaving (and don't care either!) although the humans were heard complaining about high land taxes.
After a while the flotilla reached Grecia where the rats settled for a while. Niz'tizi'ihack took control of the armies of Greece, nicked an army of Djinn and started a lucrative opium empire, amazing what the week-willed monkey things will let you get away with, until they realised the Jackals faction was hardly a stable empire and seemed to have a regard for cats that was unhealthy and moved the flotilla on to the much more impressive Viper faction. (Niz'tizi'ihack mutters something about "rats and sinking ships"). While part of the Jackals faction Niz'tizi'ihack served as Jackals ambassador first to the Tarantulas and then to the Bears.
At the Silent Whisker's first Gathering as part of the Vipers Lord Ordos very kindly granted permission for the flotilla to use the coast of Phomeravia as their new home - at the time he was surrounded by a large collection of rats from various groups asking questions like
"can we build a big wall in the middle of Berlin?" - "No"
"Can we build a huge monument to you in the middle of Berlin? It would be sort of long and thin and ..." - "No"
etc (this went on for quite a while until)...
"Can we float a large flotilla of rats off the coast of Phomeravia?" - "I'd like to see you do that".
Just to be sure Niz'tizi'ihack asked the Viper fleet quartermaster and he didn't mind either.
So after their long journey from Cathay to Phomeravia via Grecia etc. the flotilla now consists mainly of descendents of the original Cathayan Silent Whiskers (due to short rat life spans) and also many other rats who have both joined and departed along the way so in recognition of this the members of the flotilla renamed themselves the Nezumi Kami.